1. Field of the Invention
The present invention relates to a residual ink detection mechanism. More specifically, the present invention relates to a residual ink detection mechanism for detecting the amount of residual ink within an ink container of an ink jet printer.
2. Description of the Prior Art
With a conventional ink jet printer, drops of liquid ink are ejected onto a printing paper sheet for recording. An ink container for holding the ink must satisfy the following requirements:
1. The ink must not leak during vibrations or impacts in order not to contaminate the surrounding environment. PA1 2. The structure must substantially prevent evaporation of ink components to keep constant the physical characteristic of the ink, such as the surface tension and viscosity. PA1 3. An alarm must be generated for signaling the need for supplementing the ink when there is little ink left in the ink container.
FIGS. 1A and 1B show a residual ink detection mechanism using an ink container satisfying the requirements described above.
In the mechanism shown in FIG. 1A, a float 3 incorporating a magnet floats in a side channel 5 of an ink container 1, and a lead switch 4 is arranged opposite to this side channel 5. When a little ink 2 is left inside the container 1, the float 3 inside the side channel 5 descends as the level of the ink 2 lowers, so that the lead switch may be operated and the amount of residual ink may be detected. Another mechanism shown in FIG. 1B detects the amount of residual ink by a light-emitting means 6 and a photosensitive means 7 in place of the lead switch 4. When the amount of opaque ink decreases to below a predetermined level, the photosensitive means 7 receives light from the light-emitting means 6 thereby detecting the level of the residual ink. In the ink containers 1 as shown in FIGS. 1A and 1B, the residual ink detection mechanisms as shown in FIGS. 1A and 1B may be adopted.
However, a new type of ink jet printer has recently been developed wherein the ink is not under pressure, but rather a voltage is applied as necessary to eject the ink. The residual ink detection mechanisms as described above are not effectively applicable to the ink containers of the ink jet printers of this new type. This is because the ink containers of the ink jet printers of new type are flat and thin.
FIG. 2 shows such an ink container. As shown in this figure, ink 11 is filled in a flat ink bag 10 or triple-layered structure, the overall ink bag 10 is housed inside a casing 13 having a ventilation hole 12, and the ink 11 is supplied to the exterior through an outlet pipe 14 arranged inside the ink bag 10 and through a rubber stopper 15. The ink is supplied by connecting a needle 16 to the outlet pipe 14 inserted into the rubber stopper 15. The ink bag 10 comprises, for example, as shown in FIG. 3, a nylon plastic thin film 17 having a thickness of 5 to 10.mu. for external protection, an aluminum thin film 18 having a thickness of about 10.mu. for preventing evaporation of the ink and deterioration of the ink by ultraviolet radiation or the like, and an inner main bag 19 consisting of a polyethylene thin film having a thickness of 50 to 70 .mu..
In the case of a flat thin ink bag of the construction as described above, supply of fresh ink is performed by replacing the old casing with a new casing. The ink bag 10 is a flat bag, and the level shift of the ink from the full to the empty condition is thus only about 10 mm at maximum. The ink bag 10 is easily deformable by atmospheric pressure since it is a flat and flexible bag. Therefore, the ink level may be kept constant. However, such an ink bag of the flat and thin type has drawbacks in that the residual ink detection mechanisms as described above may not be used and correct detection of the amount of the residual ink is difficult.